Assessment of consistency and strength properties of clays treated with paper sludge ash-based stabilizers using the water absorption and retention rate

Abstract

Paper sludge ash-based stabilizers (PSASs) have recently been developed in Japan as sustainable construction materials for soil stabilization. PSASs are produced by the in-solubilization of heavy metals in paper sludge (PS), which is generated as a by-product of the de-inking and re-pulping of paper. PSASs can improve the stability of high-water-content clays immediately after mixing owing to their good water absorption and retention performance. However, mixture design methods that consider time variations of the water absorption and retention performance of a PSAS are lacking. Therefore, in this study, the effects of a PSAS on the physical and mechanical properties of the treated clay were experimentally investigated, considering the change in the water absorption and retention performance of the PSAS with curing time. The water absorption and retention rate, Wab, of the PSAS, is defined as the ratio of the mass of water absorbed and retained by the PSAS to its dry mass. Physical tests and cone index tests were conducted on different types of clays treated with different types of PSASs. The test results showed that different Wab values were obtained depending on the type of the PSAS and that the Wab value increased with curing time. From the experiments, it was found that the liquid limits, wL, and plastic limits, wP, of the PSAS-treated clays with different curing times could be evaluated from the Wab values of the PSAS and the particle sizes of the PSAS and untreated clays. A clear correlation was also found between the cone index, qc, and liquidity index, IL, of the treated and untreated clays. Based on the results, a new approach for mixture design was proposed. The applicability of the proposed method was investigated, and the results showed that the measured qc value of the PSAS-treated clay was close to the target qc value. The average measured qc was approximately 1.1 times the corresponding target qc. The maximum error between the measured qc and target qc values was approximately 30%.